<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>fixed problem</title>
	<style type="text/css" media="screen">
		.left-form {
			position: fixed;
			/*position: absolute;*/
			/*position: relative;*/
    	top: 0;
    	right: 0;
    	z-index:1024;
    	height: 100vh;
    	width: 50%;
    	border: 1px solid blue;
		}
		.dialog {
			position: fixed;
			left: 50px; 
			top: 146px;
			width: 50%;
			height: 500px;
			z-index: 2039;
			background-color: red;
		}
		.v-model {
			position: fixed;
	    left: 0;
	    top: 0;
	    width: 100%;
	    height: 100%;
	    opacity: .5;
	    background: #000;
			z-index: 2038;
			color: #ffffff;
		}
	</style>
</head>
<body>
	<div class="left-form">
		这是右框z-index:1024
		<div class="dialog">这是弹窗z-index: 2039;不应该我在最上面吗？</div>
	</div>
	<div class="v-model">z-index:2038;我怎么在最上面了？？？</div>
</body>
</html>